This application claims the benefit of Korean Patent Application No. 1999-67842, filed on Dec. 31, 1999, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device implementing in-plane switching (IPS) where an electric field to be applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices with light, thin, and low power consumption characteristics are used in office automation equipment and video units and the like. Conventionally, the LCD device includes upper and lower substrates that are attached together with a liquid crystal layer interposed therebetween. On exterior surfaces of the upper and lower substrates, polarizers or retardation films are formed.
By configuring the above-mentioned elements selectively, an irradiation of light and a refraction index are changed such that the LCD device has high brightness and contrast ratio. Recently developed LCD device adopts a twisted nematic (TN) liquid crystal. Since the TN liquid crystal has a characteristic of variable transmittance according to viewing angles, it""s application to a large-sized LCD device is limited.
The LCD device having the TN liquid crystal has a symmetrical transmittance in directions of right and left and an unsymmetrical transmittance in directions of up and down. The unsymmetrical transmittance results in a reversed image. Therefore, the viewing angle of the LCD device having the TN liquid crystal has a wide viewing angle in directions of right and left, but a narrow view angle in directions of up and down. Driving methods for such LCDs typically include a twisted nematic (TN) mode and a super twisted nematic (STN) mode. Although TN-LCDs and STN-LCDs have been put to practical use, they have a drawback in that they have a very narrow viewing angle. In order to solve the problem of narrow viewing angle, IPS-LCD devices have been proposed. IPS-LCD devices typically include a lower substrate where a pixel electrode and a common electrode are disposed, an upper substrate having no electrode, and a liquid crystal interposed between the upper and lower substrates. The IPS-LCD device has advantages in a contrast ratio, gray inversion, and a color shift that are connected with the viewing angle.
FIGS. 1A and 1B respectively show on and off states of a conventional IPS-LCD device.
As shown, upper and lower substrates 17 and 19 are spaced apart from each other, a liquid crystal layer 15a is interposed between the upper and lower substrates 17 and 19, and upper and lower polarizers 21 and 23 are respectively formed on each exterior surface of the upper and lower substrates 17 and 19.
On the lower substrate 19, a pixel electrode 11 and a common electrode 13 are formed to be parallel with each other and have a gap therebetween. The pixel and common electrodes 11 and 13 include a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO), and an opaque conductive metal.
In FIG. 1A, no electric field is applied between the pixel and common electrodes 11 and 13 such that the liquid crystal 15a is aligned in its early alignment state. Namely, long axes of the liquid crystal molecules 15a are aligned to be parallel with the pixel and common electrodes 11 and 13.
On the contrary, in FIG. 1B, an electric field (not shown) is applied between the pixel and common electrodes 11 and 13 such that the long axes of the liquid crystal molecules 15a are aligned to be perpendicular to the pixel and common electrodes 11 and 13.
Since the IPS-LCD device uses the electric field parallel with the substrate, a wide viewing angle is achieved. Specifically, the viewing angle of the IPS-LCD device is about 70 degrees in direction of up, down, right, and left.
The above-mentioned pixel and common electrodes may have various structures. FIG. 2 shows a plane view of the conventional IPS-LCD device.
As shown, gate and data lines 31 and 33 cross each other to define a pixel region xe2x80x9cPxe2x80x9d. In the pixel region P, a common electrode 35 including a plurality of sub-common electrodes 35b is formed to be perpendicular to the gate line 31, and a pixel electrode 37 including a plurality of sub-pixel electrodes 37b is also formed to be perpendicular to the gate line 31. The sub-common and sub-pixel electrodes 35b and 37b are parallel with each other and have gaps in an alternating pattern. Each end of the sub-pixel electrodes 37b is electrically connected with a transverse pixel line 37a, while each end of the sub-common electrodes 35b is electrically connected with a transverse common line 35a. 
Conventionally, the sub-common electrodes 35b and the transverse common line 35a are formed in a same layer to communicate with each other. Further, the sub-pixel electrodes 37b and the transverse pixel line 37a are formed in a same layer to communicate with each other. At this point, each cross point xe2x80x9cBxe2x80x9d of the sub-electrodes and the transverse lines is formed to have a round with a smooth curve.
Due to the round of the cross point B, an abnormal electric field occurs at the cross point B. Namely, when the electric field is applied between the sub-electrodes in the pixel region P, only the cross point B has a different electric field throughout the pixel region P.
Before a detailed explanation about the above-mentioned abnormal electric field, referring to FIG. 3A, a direction of an orientation film will be explained. A first axis 31a is a longitudinal direction of the gate line 31, and a second axis 33a is a longitudinal direction of the data line 33. As shown, a rubbing direction 41 of the orientation film (not shown), which is used to orientate the liquid crystal molecules, have an angle of over 90 degrees with respect to the first axis 31a and towards the second axis 33a. 
Now, the previously mentioned problem of the abnormal electric field will be explained in detail with reference to FIG. 3B. FIG. 3B is an enlarged view of a portion xe2x80x9cAxe2x80x9d of FIG. 2.
As shown, the sub-pixel electrode 37b crosses the transverse pixel line 37a in shape of a round xe2x80x9cRxe2x80x9d such that a distance between the sub-pixel and sub-common electrodes 35b and 37b varies around the rounded shape. Due to the above-mentioned variance of the distance, when an electric field 43 is applied to the pixel and common electrodes 35 and 37, an abnormal electric field 45 is formed in a gap xe2x80x9cDxe2x80x9d between the round R of the sub-pixel electrode 35b and the sub-common electrode 37b. Since the abnormal electric field 45 has a different direction from the rubbing direction 41 of FIG. 3A, the liquid crystal molecules are abnormally aligned in the gap D. The abnormal alignment of the liquid crystal molecules occurs around cross points of the sub-electrodes and the transverse lines throughout the pixel region P of FIG. 2.
Accordingly, a color dispersion occurs around the pixel region P, and a level of the gray scale changes abnormally in a middle range of the gray scale.
Accordingly, the present invention is directed to an IPS-LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an IPS-LCD device having a high luminance and a stable gray scale.
In order to achieve the above object, the first preferred embodiment of the present invention provides an in-plane switching mode liquid crystal display device, which includes a gate line and a data line on a first substrate; a pixel region defined by the gate and data lines; a switching device intersection portion between the gate and data lines; a pixel electrode and a common electrode on the first substrate, the pixel electrode having a groove around a cross point between the pixel and common electrodes; a first orientation layer on the first substrate; a second orientation layer on a second substrate; and a liquid crystal layer between the first and second substrates.
The groove has a shape of a triangle. The groove prevents a reverse electric field. The pixel electrode includes a transparent conductive material. The transparent conductive material is selected from a group consisting of indium tin oxide and indium zinc oxide. The common electrode includes an opaque metal. The gate line includes an opaque metal. The data line includes an opaque metal. The switching device includes a thin film transistor. The pixel electrode is electrically connected with a transverse pixel line. The common electrode is electrically connected with a transverse common line.
In another aspect, the present invention provides a fabricating method of an in-plane switching mode liquid crystal display device, the method includes forming a gate line and a data line on a first substrate, the gate and data lines defining a pixel region; forming a switching device intersection portion between the gate and data lines; forming a pixel electrode and a common electrode on the first substrate, the pixel electrode having a groove around a cross portion between the pixel and common electrode; forming a first orientation film on the first substrate; forming a second orientation film on a second substrate; and forming a liquid crystal layer between the first and second substrates.
The groove has a shape of a triangle. The groove prevents a reverse electric field. The pixel electrode includes a transparent conductive material. The transparent conductive material is selected from a group consisting of indium tin oxide and indium zinc oxide. The common electrode includes an opaque metal. The gate line includes an opaque metal. The data line includes an opaque metal. The switching device includes a thin film transistor. The pixel electrode is electrically connected with a transverse pixel line. The common electrode is electrically connected with a transverse common line.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.